I'd try to coordinate first, not just stand up and leave.
Worst case, the co heal will shield like a bot. So what? More DPS for me, I guess. If someone is adamant about spending so many GCDs on shielding, I'll just let them do their thing and use my resources elsewhere. It's not the end of the world for me.
And no, I was not referring to dedicated and highly coordinated groups. I was referring to all sorts of parties. SGE/ SCH is extremely strong in PUGs aswell and easy enough to handle - unless both healers stomp their foot, cross their arms and demand to be THE undisputed GCD shield healer king/ queen for the party.
